Propeller



May 31, 19,32 E. E. ARNOLD 7 1,360,522

PROPELLER Filed Dec. 27, 1930 3 Sheets-Sheet 1 in w INVENTOR FdW/h flma/a! 7ATTOiRNEY May 31, 1932. E; E. ARNOLD PROPELLER Filed Dec. 27, 1930 3 Sheets-Sheet 3 d R H mm W N 0 E \m A ms v f w/ 3 m W MN 0m T m MW Patented May 31, 1932 UNITED- ,STATES PATENT OFFICE EDWIN E. ARNOLD, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA PROPELILER Application filed December 27, 1930. SerialNo. 505,064..-

My invention relates to propellers and par- ,ticularly to the hubs of adjustable and fixedpitch propellers. i

A disadvantage of adjustable-pitch propellers has been that the support for the pro peller blade inthe hub was weak and lacking in permanent-rigidity which, at times, resulted in wear from the lack of stressed fit between blade and the hub parts when rotating. I

The high beam reaction in a propeller, due to .aerofoil resistance during rotation, combined with the centrifugal forces set up at high revolving speeds, requires that the propeller blade shall be held firmly in its mounting so that a reaction against the beam is set up, which may be termed an anti-beam reaction. When the propeller blade is turned for adjusting pitch, there should be a provision in the hub for the propeller blade to turn forward and backward, as well as a firm support for the base of the propeller blade.

Difficulty has also been experienced in securing a high joint efficiency between the several parts of propellers using materials of different moduli of elasticity. When the pro the centrifugal and aerofoil peller revolves,

the weight and air resistance forces set up by of the blades should be transmitted to the hub parts in such manner as to give safe and uniform stressing of the joints. To accom plish this result in a propeller several parts of which are made of materials having widely different moduli of elasticity, requires special compensating means to take care of the differences in stretch or deformation of the several materials under highly stressed conditions, as when an airplane propeller is being driven at high speed.

The joints between the propeller blades and hubs having generally taken the form of either one or more concentric shoulders on the base of the propeller blade engaging similar shoulders in reverse position in the hub,'or a screw-thread-of such form as to give similar engagement; Transverse surfaces are also generally provided to hold the blade in axial 'ali ment and resist lateral beam forces.

ii any such structure, when the blade is the lesser degree of deformation in the material of high modulus to which it is joined. -As an example, the propeller blade may be machined on its base with a series of rings or with a continuous thread, fitted into a hub having similar rings or threads, so that the two parts exactly fit together. When the blade is pulled away from the hub by centrifugal forces, the material of the blade will be stretched to its breaking point at the neck of the/nearest ring or convolution of thread long before any appreciablestress is felt in the core of the material or at the rings or threads remote from the force applied.

To a lesser degree, perhaps, but still having a bearing upon the highest efliciency of the joint, in propeller assemblies using a single-pitch thread between a propeller and a hub made of materials of different moduli of elasticity, the propeller blade will first .start to tear at the highest side of one of the threads, because it is at this point that the stresses first become apparent, and then travel around the thread to the lower point.

An object of my invention therefore, is to obtain firm seating of an adjustable-pitch propeller by a simple means which may be adapted to each propeller blade at low cost of material and labor.

Another object of my invention is to pro vide an improved connection between materials of difierent moduli ofelasticity.

Further objects and advantages will be apparent from the following description and accompanying drawings wherein:

Figure 1 is a view, partly in section, of a propeller assembly of a ferruled blade having a single-pitch standard thread and a point.

yieldin seat in the hub for adjustment of the pitch of the blade.

F1 2 is a cross sectional view taken on the line I-II of Fig. 1, and illustratin the offset figure of any section as obtaine with a single-pitch thread, and showing the ferrule, hub and clamping means.

Fig. 3 is a view, partly in section, of a propeller assembly having a ferruled blade provided with double-pitch rounded threads and ,a yielding seat in the hub for adjustment of the pitch of the blade.

Flg. 4 is a cross sectional view of the proeller shank shown in Fig. 3 and illustrat- 1n the symmetrical elliptical section obtamed with double-pitch threads.

Fig. 5 is a view, partly in section, of a hub assembly without adjusting means or a ferrule and provided with single-pitch standard threads.

Fig. 6 is a view, partly in section, of the adjusting means for a hub assembly in which the blade shank is not ferruled.

Fig. 7 is a sectional view of a ferrule and blade having standard threads, in which the thread angle is varied between the threads in the ferrule and those on the butt of the blade, as shown also in Figs. 1, 4 and 5.

Fig. 8 is a sectional view similar to Fi 7 but showing, in detail, the rounded threa s illustrated in Fig. 3 4

In my improved design for an adjustablepitch ropeller, a resilient member is placed in the base of the hub, and the ferrule or propeller shank is screwed into the hub. The end of the ferrule or shank fits inside the resilient member. As the .propeller is turned forward or backward, the resilient member will expand and contract, thus keeping the ferrule or shank always tight against the thread of the hub and insuring against lateral movJement at those points. It also provides a support between the shank or ferrule and the side wall of the hub, thereby insuring against transverse movement at that My invention provides three'distin'ct steps for obtaining connections of the greatest efficiency between materials having widely different moduli of elasticity, any combination of which may be used to give improved results over the present practice.

The first step comprises placing a in a'terial such as aluminum which has a modulus of elasticity falling between the moduli of 'the two materials such as steel and micarta to be connected. The effect of the difference p in stretching is thereby reduced,

The second. step consists in providing proessive increments of space between the threads of one material and the cooperating threads of another to compensate for their different moduli of elasticity by allowing a complete stretching of the material having the greater modulus, thus distributing the stress within the member of relatively lower elastic modulus.

In the event that the length of the threaded portions warrants the o oration, the threads at the inner end, or on t e end remote from the applied force, may be pre-stressed by means of a forced or shrink fit, thereby causing the threads most remote from the force applied to take up the load first and,

to a considerable extent, to distribute the uneven axial pitch is obtained by varying the angle between the cones carrying the threads.

The third step consists in-adapting double-pitch threads to a joint utilizing different angles between the male and female members. By this means, any horizontal cross-section will be a symmetrical figure about the central axis, whereas, in a single-pitch thread, the horizontal cross-section, rical figure about its own center, is out of center with the blade axis and, therefore, subject to unequal axial stress. By using threads of an even-surface pitch, it has been proved by experiment that the failures of the blade material occur at a much higher stress than when single-surface-pitch threads are emplo ed.

eferring specifically to the drawings, 1 designates a resilient member in the form of a coiled spring placed inside a socket in the hub 2 and held in place by a ring-shape clip 3. The blade may be ferruled, as shown in Figs. 1 and 3, or unferruled, as shown in Fig. 6. The yielding-seat member 1 not only keeps the threads 4 stressed in the direction of working load, thereby removing the possibility of any movement laterally, but a firm seating for the inner end of the ferrule 6 is provided, as it is interposed between the wall 7 of the hub 2 and the ferrule 6. The resiliency of the yielding-seat member 1 allows the blade 8 to be turned through a sufiicient angle to permit adjustment of the pitch of the propeller. The resilient member 1 may be used with an adjustable-pitch propeller of either type shown, that is, the ferruled or unferruled' member.

The blade is then rigidly clamped by tightening upon a bolt 30 by means of a nut 31, which bolt extends through the eyes 28, provided on the hub 2, and pulls the inset 29 partly closed, thus gripping the blade against rotation and holding it firmly against lateral or beam loading between the bending-mothe male and the female while a symmetment surfaces provided at the top and the bottom of the ferrule mounting.

In order to obtain connections of the highestefiiciency, in materials of different moduli 'of elasticity, the joint has been improved in three respects. It is understood that the joints are not limited solely to incorporation in propellers but may be employed wherever it is desired to secure an eflicient joint between substances of widely different moduli of elasticity such as steel and micarta.

One. improvement consists in joining two materials having varying moduli of elasticity such as steel and micarta through the inter mediary of a material which has a modulus of elasticity falling between those of the two materials to be connected such as aluminum. By this means, the difference in stretch is shared by the intervening material. Forinstance, if the modulus of the blade material 5 such as micarta is in the neighborhood of 1,500,000 and the modulus of hub material 2 such as steel is in the neighborhood of 30,000,000, material 5 will stretch 20 times as much per unit of stress as the material 2.

However, if ferrule material 6 such as alumi- 'num having a modulus of say 15,000,000 is placed between the materials 5 and 2, the stretch between materials 6 and 5 will only be in the ratio of 10 to 1 per unit of stress, while the ratio of 2 to 1, per unit of stress will prevail between materials 6 and 2. This latter ratio is low enough to require no further reduction, but the ratio of 10 to 1 between material 6 and 5 is still so high that, as soon as stresses are placed in the joint, the material at the point 13 will receive all the strain and will, therefore, fail at a point giving a very low over-all joint efficiency. The placing of material 6 between materials 5 and 2 makes the next step in the invention more feasible but it is not a necessary pre-requisite.

Since the materials. 6 and 5 have a stretch ratio of 10 to 1, the threads 14.- are placed on a truncated cone 5 at a slightly smaller angle than the thread 4 on the hub 2 in Fig. 5 (r the thread 16 on the ferrule 6 in Figs. 1 and 2.

, As the angle between the threads differs,

small but progressively increasing spaces will be left between the thread on the shank 5 and the threads on hub 2 or ferrule 6. This results in an eifectsimilar to the screwing together of threads of like profile but of slightly different pitch. For example, referring to Fig. 7 if the angle of the hub or ferrule is 15 and the threaded shank is approximately 4 inches long, an angle of 14 45' on the shank will give satisfactory results.

The small spaces 20 will allow the material 6 to stretch and fill up these spaces and thus, the spaces at the base 22 of the hub will be first filled up and the thread stretched, and gradually, as the spaces are filled up towards the top 23 of the hub, all the threads will take their uniform'share of the load. It is preferable that the shank 5 be forced upon the hub 2 or the ferrule 6 so that the threads at the bottom of the shank will be pre-stressed and will take their share of the load before the spaces 20, left by the variation in the angle between the thread 16 and threads 14,

An additional means of strengthening the connection between the blade shank 5 and the hub 2 or ferrule 6 is by means of a double pitch thread. Fig. 2 shows the development of a section transverse to the axis of a shank supplied with single-pitch threads. In this unsymmetrical structure, the stresses are first taken up at the high point 24 and run around the thread to the low point 25. The material will start to tear at the point 24:, as all the initial stress is taken at this point. By using double-pitch threads, as shown in Fig. 4, the figure is axially symmetrical, so that the stresses are evenly distributed between the points 26 and 27. The highest stresses occur at these points simultaneously but are much smaller than the stresses at point 24 in Fig. 2. I

It is apparent from the foregoing description that I have provided a means for securing adjustable pitch in a propeller without sacrificing any inherent strength in the materials employed and that the means is readily adaptable to propellers built according to present practice.

It is also apparent that the improved structure provides for an eflicient joint between materials having varying moduli of elasticity and subject to considerable stress.

It is understood that any combination of the embodiments shown in the drawings, may be used, and that those skilled in the art may make modifications and changes without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. In a coupling between materials of different moduli of elasticity,- means for substantially equally stressing the connections between said coupling materials comprising threads of even pitch so arranged that any horizontal cross section of the coupling will be an axially symmetrical figure.

2. In a coupling composed of materials of different moduli of elasticity, the method of equally stressing the connections between the materials of said coupling comprising pre-stressing the connections at the points remote from the force applied and varying slightly the angle between the materials of said coupling.

3. Ina pro eller blade and hub using materials of di erent moduli of elasticity and of a hub and adapted to receive the shank end of a propeller blade, said resilient member being so constructed and arranged as to compress and expand as theblade is turned, means on the hub for fastening the propeller blade in its adjusted position, and means for obtaining substantiall equally stressed connections between sai blade and said hub comprising a pre-stressed connection at the points remote from the force applied.

4. A propeller blade and hub embodying materials of different moduli of elasticity and having means for adjusting the pitch of the propeller blade and obtaining self-edjusting cam-moment reaction surfaces, said means comprising a resilient member positioned inside of a hub and adapted to receive the shank end of a propeller blade, said resilient member being so constructed and arranged as to compress and expand as the blade is turned, means on the hub for fastening the propeller blade in its adjusted position, and

means for substantially equally stressing the connections between said blade and said hub comprising threads of even-surface pitch, whereby any hOIlZOl'll'fll cross section of the 5 blade shank will be a symmetrical figure about its axis.

5. A propeller structure comprising a blade, a hub and a ferrule composed of materials having difl'erent moduli of elasticity, and means for adjusting the pitch of the pro peller blade and obtaining self-adjusting cam-reaction surfaces, said means comprising a resilient member positioned inside of a hub and adapted to receive the shank end of a propeller blade, said resilient member being so constructed and arranged as to compress and expand as the blade is turned, means on the hub for fastening the propeller blade in its adjusted position, and means for substantially equally stressing the connections between said blade and said hub comprising pre-stressed connections at the points remote from the force-applied and a.slightly varied angular connection between the blade and the ferrule.

blade is turned, means on the hub for fastening the propeller blade in its adjusted position, and means for substantially e ually stressin the connections between said lade and said ferrule comprising threads of evensurface pitch so arranged that any horizontal cross-section of the blade shank will be a symmetrical figure.

7. Means for connecting materials of dif ferent moduli of elasticity comprising a material the modulus of which falls between the moduli of the two materials of different moduli to be connected together, said material having the intermediary modulus being disposed between the other two materials.

8. Means for connecting materials of different moduli of elasticity comprising a material the modulus of which falls between the moduli of Qhe two materials to be connected, cooperating threads on each of the materials, said material of intermediary modulus being ,placed between the other two materials, the

cone an 1e of the thread connecting the material 0% intermediate modulus to the--mate' rial of lowest modulus being slightly greater than the cooperating thread of the material of lowest modulus.

9. A. propeller blade and hub embodying materials of different moduliof elasticity and havin means for adj ustin the itch of the prope ler blade and obtaining 'se f-adjusting beam-moment reaction surfaces, said means comprising a resilient member positioned inside of a hub and adapted to receive the shank end of a propeller blade, said resilient member being so constructed and arranged as to compress and expand as the blade is turned, means on the hub for fastening the propeller blade in its adjusted position, and means for substantially equally stressing the connections between said blade and said hub comprisin threads of different axial pitch.

10. n a coupling composed of materials of different moduli of elasticity, the method of equally stressing the connections between 1 the materials of said coupling comprising varyin slightly'the angle between the materials 0 said coupling.

In testimony whereof I have hereunto subthis 23rd day of December,

scribed my name 1930.

EDWIN E. ARNQLD.

6. A propeller structure comprising a blade, a hub and a ferrule composed of materials of a different moduli of elasticity, and means for adjusting the pitch of the propeller bladeand for obtaining anti-beam re- 

